Method of advancing a prestressed concrete bridging structure

ABSTRACT

A method of advancing a prestressed bridging structure over a pier in which the pier is provided with a sliding surface being a part of a cylinder the concavity of which is directed toward the pier and whose generatrix is perpendicular to the vertical plane containing the bridge axis, whereby support pieces introduced between the bridging structure and the sliding surface on that side of the pier whence the structure is advancing will ride up the surface and carry the structure over the surface.

United States Patent Launay 451 Aug. 22, 1972 [54] METHOD OF ADVANCINGA 3,367,074 2/1963 Vanich ..52/223 PRESTRESSED CONCRETE BRIDGING STRUCTURE FOREIGN PATENTS OR APELICATIONS Inventor: Pierre y, 108 Boulevard de la 811,839 4/1959 Great Britain ..14/13 Reme France Primary Examiner-Frank L. Abbott 22 i July 23, 1970 Assistant ExaminerJames L. Ridgill, Jr. Attorney-Cameron, Kerkam and Sutton [21] App1.No.: 58,864

[ ABSTRACT [30] Foreign Application Priority Data A method of advancing a prestressed bridging structure over a pier in 'which the pier is provided with a Aug. 26, 1969 France ...6929212 Sliding Surface being a p of a cylinder the concavity of which is directed toward the pier and whose [52] US. Cl. ..52/173, 52/223, 52/745 generatrix is perpendicular to the vertical plane com [51] IIiLCl. ..E04h 14/00, E046 3/10 taining the bridge axis whereby Support pieces [58] Field of Search.... 14/13, 21; 52/745, 223, troduced between the bridging Structure and the 1i 227-229, ing surface on that side of the pier whence the struc- 173 ture is advancing will ride up the surface and carry the structure over the surface. 56 R f C'ted 1 e erences l 1 Claim, 3 Drawing Figures UNITED STATES PATENTS 3,570,207 3/1971 Launay ..-.....52/745 METHOD OF ADVANCING A PRESTRESSED CONCRETE BRIDGING STRUCTURE This invention relates to a method of advancing a prestressed concrete bridging structure. It applies more particularly to advancing a structure, e.g. an aqueduct or a bridge deck, by pushing the same.

A prestressed concrete bridging structure of this type generally consists of prestressed concrete sections which are successively cast on a prefabrication zone and then successively interconnected with temporary prestressing of the connection between two adjacent sections, the assembly then being progressively pushed from an abutment by sliding on the piers and abutments after each new section has been added. Thetemporary prestressing can then be removed after final prestressing of the assembly in its final position.

Advancing methods are known wherein the connected assembly slides on the piers or abutments with the interposition of sliding supports which remain connected to the assembly during the movement and which slide on slide surfaces disposed on the piers or abutments, and the connected assembly is pushed by incremental thrusts, each incremental cycle successively comprising a thrusting stage, followed by lifting of the assembly, and then lowering of the assembly which then once again rests on the piers and abutments through the agency of the sliding supports.

This system has the disadvantage that there is a considerable waste of time as the structure progresses. The reason for this is that the length of each incremental thrust cannot exceed the length of the slide surface on a pier, and after each incremental thrust the assembly must be lifted away from each pier or abutment so that the sliding supports can be shifted and brought into position for a fresh thrust.

These lifting and lowering operations are relatively time-consuming and expensive and have to be employed whenever the structure has progressed by approximately just one meter.

The present invention provides a practically continuous advance of the structure and according to the invention the sliding surface of each pier or abutment consists of a cylindrical surface whose generatrices are perpendicular to the axial plane of the structure and whose directrix is a continuous curve the concavity of which faces the corresponding pier or abutment, and the sliding of the structure is produced by continuous thrusts of an amplitude greater than the dimension of the pier heads in the direction of advance, the sliding supports being successively introduced between the structure and the upstream part of each slide surface, and collected at the downstream part of each slide surface.

The invention will now be described in greater detail with reference to one exemplified embodiment illustrated in the drawings.

FIG. 1 diagrammatically illustrates a deck being advanced by the method according to the invention.

FIG. 2 is a detail of the connection between successive sections.

FIG. 3 is a partial diagrammatic longitudinal section of the top part of an intermediate pier.

Referring to FIG. 1, the bridge comprises an abutment pier 1 and intermediate piers 2, 3, 4 etc. The bridge deck consists of successive sections 6, 7 l2,

which are cast with temporary longitudinal prestressing at a prefabrication zone 13. Section 16 is being made in the drawing. As the deck advances, the successive sections are connected together as shown in FIG. 2. The assembly formed by two adjacent sections is temporarily prestressed by cables 14.

The abutment pier l is provided with a framework 17 which acts as a support for two long-stroke hydraulic jacks 18 each disposed on either side of the deck. The rod of each jack 18 is connected by a tie-rod 20 to a securing bracket 19 fixed on the section.

Referring to FIG. 3, the top part of an intermediate pier 2 comprises a curved slide member formed by a slab 23 of concrete covered by a stainless steel plate 24.

The top surface of the slab 23 and the plate 24 have a cylindrical shape with horizontal generatrices perpendicular to the central plane of the structure. The

directrix of this cylindrical surface in the axial plane of the structure is an arc of a large-radius .circle whose center is situated on the pier axis, i.e., the slide member 22 is symmetrical with respect to the pier axis.

The slabs 25 and 26, the height of which is slightly less than the lowest part of the slide member 23, are disposed on either side of the member 23 in the direction of movement 27.

The pier 2 is equipped with a set of hydraulic jacks 31 disposed in special housings and each resting on a neoprene distribution plate 32.

The bridge deck 8 rests on the slide member 23 by means of independent slide shoes 35, 36, 37, 38. Each of these shoes, e.g., shoe 35, consists of a slab of reinforced elastomer 39, the bottom surface of which is covered by a sheet of cellular tetrafluoroethylene 40.

The height of arc of the curved slide member 23 is greater than the maximum crushing deformation of the elastomer. Thus the slide shoes 35, 36, 37 and 38 can easily slide between the deck 8 and the slide member 23. Thus the shoe 35 which is initially placed on the slab 25 is pushed manually or by mechanical means until it is in contact with the shoe 36. As soon as it comes into contact with the underside of the deck 8 it will be driven because its coefficient of friction on the deck underside is very much greater than its coefficient of friction on the plate 24 of the slide member 22.

The shoe 36 has been driven and starts to participate in supporting the structure. The shoe 37 is completely engaged. The shoe 38 is about to disengage; as soon as it rests freely on the slab 26, it will be returned to the position of the shoe 35.

The sliding of the structure is practically continuous and with no loss of time. The continuity of advance is limited only by the jack stroke, which can be made very long, or by the time required for connecting successive sections of the bridge deck. The operations of lifting and lowering the deck are replaced simply by shifting a slide shoe from the exit end to the inlet end of the slide members 22.

Of course the invention is not limited solely to the above-described embodiment, but also covers constructions differing therefrom only in detail.

For example, the longitudinal profile of the slide member 23 may include a central rectilinear part between two curved parts. Similarly the longitudinal profile need not necessarily be strictly symmetrical with respect to the pier axis but may, for example, have a slight incline in the direction of introduction of the shoes and a more sloping incline in the portion where the shoes are disengaged.

I claim: i

1. Apparatus for advancing a prestressed concrete bridging structure resting on abutments and intermediate piers, the structure consisting of prestressed concrete sections cast successively at a prefabrication zone and successively connected to one another with prestressed connection between two adjacent sections, the structure being progressively advanced from one of said abutments after each addition of a new section by sliding on slide surfaces disposed at the top of each pier or abutment, supports interposed between the structure and the slide surface, said supports comprising a bottom sliding surface in contact with the slide surface and a top surface having a high coefficient of friction in contact with the structure, the improvement in which the sliding surface of each pier or abutment includes a cylindrical surface whose generatrices are perpendicular to the axial plane of the structure and whose directn'x is a continuous curve the concavity of which faces the corresponding pier or abutment, the sliding of the structure being produced by continuous thrusts of an amplitude greater than the dimension of the pier heads in the direction of advance, at least one of said sliding supports having a maximum crushing deformation less than the length of the arc of said cylindrical surface being successively introduced between the structure and the upstream part of said slide surface, and discharged at the downstream pan of said slide surface. 

1. Apparatus for advancing a prestressed concrete bridging structure resting on abutments and intermediate piers, the structure consisting of prestressed concrete sections cast successively at a prefabrication zone and successively connected to one Another with prestressed connection between two adjacent sections, the structure being progressively advanced from one of said abutments after each addition of a new section by sliding on slide surfaces disposed at the top of each pier or abutment, supports interposed between the structure and the slide surface, said supports comprising a bottom sliding surface in contact with the slide surface and a top surface having a high coefficient of friction in contact with the structure, the improvement in which the sliding surface of each pier or abutment includes a cylindrical surface whose generatrices are perpendicular to the axial plane of the structure and whose directrix is a continuous curve the concavity of which faces the corresponding pier or abutment, the sliding of the structure being produced by continuous thrusts of an amplitude greater than the dimension of the pier heads in the direction of advance, at least one of said sliding supports having a maximum crushing deformation less than the length of the arc of said cylindrical surface being successively introduced between the structure and the upstream part of said slide surface, and discharged at the downstream part of said slide surface. 